Photosynthesis is the biological process that converts electromagnetic energy into electrochemical energy through light and dark reactions. Photosynthesis occurs in specialized organelles in green algae and higher plants called chloroplasts. The chloroplast is enclosed by a double membrane and contains thylakoids, consisting of stacked membrane disks (grana) and unstacked membrane disks (stroma). The thylakoid membrane contains two key photosynthetic components, photosystem I and photosystem II, designated PSI and PSII, respectively.
Electrical studies of photosynthetic complexes were pioneered by Lee and Greenbaum at Oak Ridge National Lab. Lee, I., et al., Phys. Rev. Lett. 79, 3294 (1997); Greenbaum, E., Science 230, 1373 (1985); Lee, I., et al., J. Phys. Chem. B 104, 2439 (2000). These workers have chemically precipitated Pt onto the electron donating site on the surface of a complex and then used the platinized complex to generate H2. They have also measured the orientation statistics of complexes on hydrophilic substrates and observed a photovoltage using Kelvin force microscopy. Greenbaum, E., Bioelectrochemistry and Bioenergetics, 21:171, 1989; Greenbaum, E., J. Phys. Chem., 94:6151, 1990; Lee, I., Proc. Natl. Acad. Sci. USA, 92:1965, 1995; Lee, I., et al., 11(4):375, 1996. See, also, U.S. Pat. No. 6,162,278, entitled Photobiomolecular Deposition of Metallic Particles and Films, Hu, Dec. 19, 2000.
Fabrication of molecular circuits is presently beyond the resolution of conventional patterning techniques such as electron beam lithography. However, positioning of molecules with sub nanometer precision is routine in nature, and crucial to the operation of photosynthetic complexes. Photosynthetic complexes, for example, are optimized to funnel energy from a molecular antenna to a reaction center where charge is generated. Natural protein scaffolds control the exact placement and orientation of optically and electronically active molecular components. Photosynthetic complexes possess a combination of size and functionality that has been optimized by evolution. In a typical complex such as that found in the purple bacterium Synechococcus Elongatus, absorbed photons are harvested within 100 ps of the absorption of a photon with an overall quantum yield of 98%. Photovoltages of 1 V are generated across the complex and the power conversion efficiency is approximately 40%. Schubert, W. D., et al., J. Mol. Biol. 272, 741-768 (1997). Indeed, natural biomolecular complexes exceed the efficiencies of even the best artificial photovoltaic devices.
The prior art, however, has failed to describe a high efficiency photoconversion structure for trapping and converting incident light to electrical energy suitable for nanometric electronic devices. A need in the art remains for solid state photosensitive devices which interface protein-based molecular components of photosynthesis with conventional electronics including photovoltaic devices which convert light into photocurrent and thereby supply electrical power to a circuit.
Accordingly, a key object of the invention described herein is the solid state incorporation of light harvesting complexes into functional devices including devices which employ single photosynthetic complexes.1 1 The prior art also fails to contemplate organic layers incorporated into a solid state photosensitive device comprised of a Light Harvesting Complex as described herein.